Pixel diameter

The size of an entire tile. (help) Example Image To check the diameter of an existing screentone use the marquee tool (M) and measure the size of a screentone tile.

Angle

The angle between dots. (help) Example Image This is usually 45 degrees in manga but you can check an arbitrary angle using the ruler tool (I)

DPI

Pixels per inch. (help) Example Image To check your document's DPI go to Image > Image size
(Ctrl + alt + I)

Shape

The shape of the screentone dots. (help) Example Image There are six screentone shapes in photoshop:
round, diamond, ellipse, line, square and cross.

How to use:

  1. In a new layer, paint the area you want to cover with a screentone using the appropiate gray shade.
    2. Example Image
  2. Copy the gray layer into a new document. Turn your image mode to grayscale, and then to bitmap
    3. Example Image
  3. Select your DPI and as method use Halftone Screen. Then the rest of the paramenters including the calculated frequency value.
    4. Example Image
  4. Copy the generated screentone in place.
    5. Example Image